1. Field of the Invention
The present invention relates to an image forming apparatus.
2. Description of the Related Art
FIG. 1 is a cross-sectional view of a conventional image forming apparatus and FIG. 2 is an exploded cross-sectional view of a portion A of the image forming apparatus of FIG. 1.
Referring to FIGS. 1 and 2, the image forming apparatus includes a printing unit 10, an exit path 20, and a reverse path 30. A guide member 40, which has a first side 41 and a second side 42, is installed at a point where the exit path 20 meets the reverse path 30. Paper stacked in a paper cassette 80 is input into the printing unit 10 by means of a pickup roller 90 and a feed roller 60. The printing unit prints an image on the paper. The paper on which the image is printed by the printing unit 10 passes through the first side 41 of the guiding member 40, is guided toward the exit path 20, and is then released onto an exit tray 55 by a rotating exit roller 50. The reverse path 30 reverses the paper, one surface of which has an image printed thereon, so that an image can be printed on the other surface and then supplies the paper to the printing unit 10. The reverse path 30 is branched out from the exit path 20 and extends to the feed roller 60.
The printing unit 10 makes it so the paper, to which toner adheres by an electrostatic force, passes between a heating roller 71 and a pressure roller 72, so that the toner is fixed onto the paper. Such a process is an image fixing process which is the final process performed by the printing unit 10 to form an image on paper using electrophotography.
FIG. 2 illustrates the heating roller 71 and the pressure roller 72, which make up of a fixing unit 70. The paper passing between the heating roller 71 and the pressure roller 72 contacts the first side 41 of the guide member 40. Since the guide member 40 is fixed, the paper is guided toward the exit path 20, being bent along the first side 41. In this respect, if the paper repeatedly contacts the first side 41, miniscule shreds of paper, toner residue, and dust stick to the first side 41.
A process in which the toner residue sticks to the first side 41 will now be described. In the process, paper, one surface of which has an image or text printed thereon, is provided. When the paper passes through the fixing unit 70 and heat and pressure are applied to the paper, the toner fixed to the surface melts and becomes soft. In this case, if the paper contacts the first side 41, the paper's surface rubs against the first side 41 and the toner fixed on the paper adheres to the first side 41. Such a phenomenon is more serious during duplex printing. This is because one surface of the paper which has an image printed thereon is again input into the printing unit 10 along the reverse path 30 and again heated by the fixing unit 70 before heat, which was applied to the paper by the fixing unit 70, has been completely cooled.
If toner waste or miniscule shreds of paper is continuously accumulated on the first side 41, there is a higher possibility for a paper jam to occur when paper passes through the first side 41. In other words, when toner is irregularly accumulated on the first side 41 to form irregular toner build-up thereon, the top of the paper may not smoothly pass by the first side 41 due to being caught on the irregular toner build-up.
Meanwhile, the guide member 40 is installed adjacent to the fixing unit 70, as shown in FIG. 2, and is thus maintained at a higher temperature by the heated fixing unit 70 than other elements of the image forming apparatus. Toner is typically formed of colorant resin and thus may be sticky when the toner is not completely cooled. Therefore, if paper rubs strongly against the first side 41 to which toner is adhered, a paper jam may also be caused.
Also, the paper jam may occur in the exit path 20. As mentioned above, toner sticking to the first side 41 is softened by the heat of the fixing unit 70 and thus may be separated from the first side 41 and adhere to the top of the paper when the top of the paper rubs on the first side 41. When the top of the paper rubs against a highest point B of the exit path 20, the course of the paper changes and the toner adhering to the top of the paper may rub off onto the highest point B at this time. If the toner continuously sticks to the highest point B, the top of the paper becomes caught by the highest point B, and as a result, paper jams may occur.
To prevent the occurrence of a paper jam, it has been suggested to install a plurality of idle rollers (not shown), which rotate when paper contacts these rollers, at the first side 41 of the guide member 40. However, the installation of the idle rollers increases the number of elements in manufacturing an image forming apparatus, thereby increasing the manufacturing costs.